1. Field of the Invention
The present invention relates to effluent removal from towers and stacks and particularly to heat removal from cooling towers. Gaseous fluid streams are selectively directed by vertical slot inlet and control means to produce a vortex flow regime within a chimney of said tower or stack to entrain and accelerate gaseous fluid streams flowing therein through an orifice from within a lower cavity portion. The invention provides heat or other effluent constituent removal such as heat transfer from a cooling fluid and removal of pollutants when embodied such as in a natural draft cooling tower which is either of the nature of a wet or dry system.
2. Description of the Prior Art
Utilization of fluid streams, usually ambient or forced air, to provide a means for removing heat or, more particularly, for cooling a condenser, or other heat exchanger, has been described in the art. U.S. Pat. No. 1,627,713 to Seymore (1927) discloses directing air, preferably tangentially, into the base of a cooling tower above the coolant to create rotative movement and thus more efficient cooling. In addition, Seymore discloses that exhaust means may be provided upon the walls of the tower to discharge at least a portion of the effluent axially.
British Specification No. 418,320 to Mouchel et al. (1934) depicts a cooling tower, which incorporates apertures in the walls to create a substantially horizontal flow of air and has for a purpose the reduction of precipitation in the surrounding atmosphere. It is stated that this embodiment, however, reduces the cooling efficiency of the tower.
Mouchel et al. also suggested incorporating nozzles within said apertures, to distribute air well inside the wall. Subsequently, Mouchel et al., in British Specification No. 629,368 (1949), described the nozzles of British Specification No. 418,320 as being arranged within the tower near its mouth and further disclosed the introduction of air, of suitable temperature, towards or away from the axis of the tower.
To reduce the dimensions and environmental impact of stacks or cooling towers, Hosking et al., in British Specification No. 525,702 (1940), suggested submerging the tower below ground level and introducing air through the base of the tower to create a kinetic effect in combination with the effluent ejected from a stack which is axially and centrally positioned. The stack extends upward and terminates at a restricted neck section of the tower. Alternative exit holes were provided in the tower sidewalls below the mouth of the stack.
Within the last decade, with the advent of large electric generating plants, which range in output from 600 megawatts (MW) for fossil-burning plants to 1,200 MW for nuclear plants and which have large cooling requirements associated therewith, and with the advent of environmental constraints, mechanical and natural draft cooling towers have become a primary means of cooling power plant condensers. The dimensions of natural draft cooling towers, which are associated with and result from the need to obtain adequate cooling capacity, may require, for example, a base diameter of 400 feet and a height of about 500 feet. The dimensions of such towers have become important factors in siting such fossil fuel and nuclear plants.
As previously stated, plants of this size category require large amounts of cooling capacity by means of condenser cooling water. A 1,000 MW fossil fuel plant, for example, may require approximately, 500,000 gallons per minute (gpm) of cooling water, while a similarly sized nuclear plant may require 750,000 gpm. Such quantities of water withdrawal from a body of water, accompanied by the heated water discharge, can have significant local effects on the biota of almost any river or lake near which the plant may be sited. Environmental regulations have been promulgated which have resulted in the use of evaporative towers, commonly known as wet cooling towers, which are of the natural draft or mechanical draft type. These towers require approximately one-fiftieth the amount of water withdrawal from a body of water as is required by an open-cycle type of cooling means for power plant condensers.
Mechanical draft cooling towers are much shorter than natural draft towers. Such towers are approximately 60-70 feet high but occupy significantly more land area in order to provide the same amount of cooling. Large amounts of energy are required to drive fans which provide the draft for the evaporative action. Further, the resultant effective height of the vapor plume from a mechanical draft tower is closer to ground level than that from a natural draft tower and consequently presents the possibility of ground fogging and icing which is frequently unacceptable.
In an effort, therefore, to reduce electric power consumption, to reduce noise and to reduce operation and maintenance costs associated with mechanical draft cooling towers, power plant designers have, in many cases, turned to natural draft cooling towers which, at present, provide cooling almost exclusively by evaporative means. The evaporative process involves the use of atmospheric cooling air which passes through heat transfer passages in the fill below the chimney portion of the structure and which entrains a small fraction of the condenser circulating water which has evaporated. The remainder of the circulating condenser water is thereby cooled. The warmed atmospheric air together with the entrained evaporated circulating condenser water rise, because of thermal buoyancy, until being discharged from the mouth of the chimney. As has been previously stated, to achieve adequate movement of this moist air mass within the tower, a conventional natural draft tower for a 1,000 MW plant, for example, may require a base diameter of about 400 feet and a height of about 500 feet. The size of the resulting structure may be considered to be a severe visual impact which is further compounded when there are several plants at a given site, each with its own cooling tower.
British Specification No. 907,852 to National Research Development Corporation (1962), describes an effort to increase plume discharge height from a stack. Pipes are arranged about the outer circumference of the stack mouth to deliver compressed air, which is directed upwardly. The embodiment contemplates operation with respect to wind velocity and direction to prevent depression of the plume below the top of the stack.
U.S. Pat. No. 3,498,590 to Furlong (1970) discloses the introduction of air, about the periphery of the lower portion of a tower, whereby the air so directed has a substantial direction parallel to the circumferential direction of the periphery as guided by partitions. It has, as an object, the direction of the gas in a spiral flow about the coolant sections by means of the partitions.
Spangemacher, in U.S. Pat. No. 3,846,519 (1974), introduces, within the cooling section, dry warm air in a direction opposite to the flow of water, which is acting as a means of coolant, to achieve more efficient cooling. Brown, in U.S. Pat. No. 3,749,379 (1973), found that by increasing the cross-sectional area of the exhaust port, in conjunction with auxiliary fans within the tower sidewalls, a substantial increase in the height of the plume could be achieved.
Of further interest are Greber, U.S. Pat. No. 3,385,197 (1973), and Stephens, U.S. Pat. No. 3,965,672 (1976). Greber uses a roof, or wind ejector, over the mouth of the tower to increase the draft of the tower. Stephens introduces air tangentially, which air is upwardly directed into the tower through the sidewalls, to reduce the necessity of wind ejectors which are embodied as roofs. Stephens allows ambient air to enter the tower base through curved slots, which requires that the tower be shaped in an L-shape with a well-rounded corner so the wind is accelerated up the sidewalls of the tower.
Rogers, U.S. Pat. No. 4,031,173 (1977), discloses a means for the generation of power and for discharging air through nozzles arrayed on the inside walls at the throat of the tower to augment and enhance the natural draft within a tower.
Finally, in U.S. Pat. No. 4,070,131 to Yen, an embodiment designed to provide means for driving a wind turbine generator, by means of the tangential admission of air is disclosed. The driving air force is introduced through and directed by means of vertically extending vanes which define a tower-like structure, to create a vortex flow, which draws ambient air into the bottom of the structure, to drive a horizontal turbine. A spiral configuration to create the vortex flow is also disclosed.
The present invention provides means for significantly reducing, for example, both the height and diameter of natural draft evaporative or dry cooling towers, for a particular cooling capacity, as compared to conventional natural draft evaporative or dry towers while retaining, and, at times increasing, the effective height of the vapor plume, in the case of evaporative towers. In the case of any tower or other stack, the objectives may be obtained by means of the creation of a stable confined effluent entraining vortex, as contemplated by the present invention. Similarly, a cooling tower of a given size, which uses the teachings of this invention, will have a significantly increased cooling capability compared to a comparably sized conventional cooling tower which does not use these teachings. If forced gaseous fluid streams, which may contain flue gas, are utilized as an auxiliary means to produce the confined vortex, the present invention may result in further benefits by providing the means for reduction of removal efficiency requirements for precipitators and sulfur dioxide scrubbers which are used for cleaning the flue gas from fossil fuel plants. It may provide more effective tower drift removal, elimination of smoke-stack structures and the elimination of reheat requirements for the gases emanating from wet process scrubbers. Furthermore, by adopting the teachings of the present invention, operating costs and maintenance costs may be decreased because of reduction of auxiliary equipment currently utilized in existing facilities. Those and other features and advantages are set forth more fully hereinafter in the following Summary of the Invention.